In the course of packaging and assembling electronic circuits and components, it is common practice to attach a circuit component, such as an integrated circuit die, to a support member, such as substrate or lead frame. Very often, the form of attachment involves the application of a prescribed quantity of a die attachment adhesive material, as diagrammatically illustrated in FIGS. 1 and 2, which shows an individual circuit die 10 attached to an underlying substrate 11 by way of a measured quantity of adhesive material 12 therebetween. The adhesive material typically takes the form of a medium to high viscosity material (often paste like), such as a polymeric, silver-filled glass, epoxy and the like, which is deposited onto the support substrate from a single port or multi-port adhesive applicator tool.
As shown in FIG. 3, such a tool customarily comprises a computer controlled step and repeat, pick and place type unit 20, having a dispensing head 22, located at the end effector position of a position arm 24, and including one or more dispensing nozzles or tubes 26 through which the adhesive material is deposited onto the substrate 11 for die attachment.
Among crucial factors in ensuring integrity of the attachment of the die to the substrate are the type, volume and pattern of the adhesive material that is dispensed onto the support substrate. An inexact volume or pattern of deposited adhesive may: 1--result in a device that fails assembly inspection, 2--fail to provide adequate electrical and/or thermal contact with the substrate, and 3--cause the device to fail mechanically in the field.
FIGS. 4-7 illustrate various adhesive dispenser tool port patterns currently used in the industry, including the single needle nozzle of FIG. 4, the multi-needle nozzle arrangement of FIG. 5, the star-grooved configuration of FIG. 6, and the stamp transfer groove pattern of FIG. 7. An evaluation of these respectively different dispensing port configurations by the present inventors has led to the conclusion that the multi-needle arrangement provides the most exact and repeatable dispense volume and pattern for the adhesive, and should be used for high reliability products, including those which must conform with standards for military applications.
Because a multi-needle adhesive applicator performs a `single shot` delivery of adhesive from plural dispenser ports into a prescribed `dot`-like pattern on the target substrate, the number, port diameter, placement, and finish of the needle nozzles of a multi-needle adhesive dispensing tool are critical to the tool's performance. Our analysis of currently available multi-needle tools has revealed that such tools suffer from poor fillet coverage, such as illustrated at regions 31 and 32 in FIG. 8, and the presence of an unacceptable number and size of voids, as shown at 33 in FIG. 9. (Customary practice dictates that the adhesive fillet must be present along at least 75% of the die edge, and x-ray voiding must not exceed 50% of the die area.)